Coated glass fibre mesh fabric with reduced gross heat of combustion

ABSTRACT

The invention is drawn to a glass fiber mesh fabric coated with an organic polymer coating having a reduced gross heat of combustion (less than 3.0 MJ/kg), said polymer coating comprising (i) from 60 wt % to 99.9 wt % of poly(vinylidene chloride) (PVDC) or a copolymer thereof; and (ii) from 0.1 wt % to 40 wt % of a formaldehyde-based resin selected from melamine-formaldehyde resins, phenol-formaldehyde resins, urea-formaldehyde resins or a combination thereof. The invention also provides a method for producing such a coated glass fiber mesh fabric.

The present invention is drawn to a glass fiber mesh fabric for use as reinforcement in External Thermal Insulation Complex Systems. The glass fiber mesh fabric is coated with an organic polymer coating based on PVDC.

Glass fiber mesh fabrics are currently used in External Thermal Insulation Complex Systems (ETICS) to reinforce the render coating and facilitate application thereof to the underlying thermal insulation product (foam, glass wool, etc.). Such glass fiber mesh fabrics are generally coated with rubber coatings, typically SBR rubber, to provide the fabric with mechanical strength and to protect the glass fibers against the alkalinity of the render composition.

Most of the member countries of the European Union have adopted the harmonized Euroclass system of reaction-to-fire performance of building products. The background of the harmonization process lies on the Commission Decision 94/611/EC implementing Article 20 of Directive 89/106/EEC on construction products in the field of fire safety. The Euroclass decision includes a classification system for building products based on their reaction-to-fire performance. It additionally defines the test methods according to which construction products shall be categorized. To be classified in class A2 (Products of natural stone, concrete, bricks, ceramic, glass, steel and other metallic products containing small amounts of organic compounds) of the Euroclass fire rating system a glass fiber mesh fabric must have a gross heat of combustion (PCS, French acronym for Pouvoir Calorifique Supérieur), measured according to EN ISO 1716:2010, of at most 3 MJ/kg.

Commonly known SBR-coated glass fiber mesh fabrics with a loss on ignition (L01) of about 20% have a PCS of about 7-8 MJ/kg and consequently do not comply with the above-mentioned European regulations.

Reducing the LOI of SBR-coated glass fiber meshes to decrease their PCS is not a satisfactory solution because it results in very poor mechanical resistance of the end products.

The idea underlying the present invention was to replace the prior art SBR-based coatings by coatings having lower PCS values.

PVDC was one of the most promising candidate for such a replacement. PVDC and copolymers thereof are a group of thermoplastic polymers commonly used in the packing industries. They have excellent gas and water tightness, very good mechanical performances, satisfactory fire resistance and low combustion heat. Replacing SBR with equivalent amounts of PVDC however leads to end-products having satisfactory PCS values but which are too stiff to be rolled.

Decreasing the LOI of PVDC-coated glass fiber meshes to reduce stiffness and cost was also unsatisfactory because the mechanical properties of the resulting fabrics were low.

After extensive research the Applicant found that it was possible to improve the mechanical performances of PVDC-coated glass fiber mesh fabrics by mixing the PVDC latex with low amounts of heat-curable formaldehyde-based resins.

Adding formaldehyde-based resins to the PVDC binder desirably increases the mechanical strength of the resulting coating thereby allowing reduction of the overall LOI and in particular reduction of the amount of PVDC required, which is very interesting from an economical point of view because PVDC is a rather expensive polymer.

The present invention is therefore drawn, in a first aspect, to a glass fiber mesh fabric coated with an organic polymer coating, said polymer coating comprising

-   -   (i) from 60 wt % to 99.9 wt % of poly(vinylidene chloride)         (PVDC) or a copolymer thereof;     -   (ii) from 0.1 wt % to 40 wt % of a formaldehyde-based resin         selected from melamine-formaldehyde resins, phenol-formaldehyde         resins, urea-formaldehyde resins or a combination thereof.

The above percentages should be understood to be based on the total amount of organic polymer coating. The sum of these percentages does not necessarily amount to 100% because, as will be explained hereafter, the organic polymer coating may further comprise a plastifying polymer and other optional adjuvants commonly used in the field of polymer coatings for construction products.

The organic polymer coating is preferably free of substantial amounts of a mineral flame retardant. The uncoated glass fiber mesh fabric of the present invention may be any open glass fiber fabric currently used for the production of SBR-coated glass fiber mesh fabrics.

It may be a woven or knitted fabric. Its specific weight is preferably comprised between 30 and 500 g/m², more preferably between 50 and 300 g/m², and most preferably between 100 and 150 g/m².

The size of the mesh openings is preferably comprised between 1 mm² and 15 cm².

The warp and weft tensile strength of the mesh fabric measured on stripes (5 cm×30 cm) is comprised between 400 N and 10 000 N.

The organic polymer coating may be applied to the uncoated glass fabric without any pretreatment. The total amount of organic polymer coating may be expressed as the loss-on-ignition (LOI), measured according to EN ISO 1887 of the final polymer-coated fabric. The organic polymer coating generally comprises between 6 wt % and 20 wt %, preferably between 7 wt % and 15 wt %, and more preferably between 8 and 12 wt % of the final coated glass fiber mesh.

Polymers of vinylidene chloride are the main component of the organic polymer coating. This term includes homopolymers of vinylidene chloride (PVDC) and copolymers of vinylidene chloride and of at least another comonomer (PVDC-based copolymers). PVDC-based copolymers are preferred. Comonomers are preferably selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, acrylonitrile, methacrylonitrile, unsaturated carboxylic acids, vinyl chloride. PVDC-based copolymers generally comprise from 75 to 98 wt %, preferably 80 to 95 wt % of vinylidene chloride monomer units and from 2 to 25 wt %, preferably from 5 to 20 wt % of comonomer units.

As explained above the organic polymer coating must contain, in addition to the PVDC or PVDC-based copolymer, a thermoset formaldehyde-based resin, preferably selected from melamine-formaldehyde resin, phenol-formaldehyde resin, urea-formaldehyde resin and combinations thereof. This resin is added to the coating composition in the form of a non-cured aqueous solution of an oligomeric resin prepared by prepolymerisation of formaldehyde and phenol, melamine or urea. It is completely polymerized and cured in situ by heating.

The organic polymer coating preferably comprises from 0.1 to 10 wt %, more preferably from 0.5 to 8 wt %, and most preferably from 1 to 4 wt % of melamine-formaldehyde resin, phenol-formaldehyde resin, urea-formaldehyde resin or a combination thereof.

The Applicant has observed that replacing styrene-butadiene rubber by a PVDC based polymer coating, resulted in a stiffer final product. To reduce the stiffness of the organic polymer coating and of the final coated mesh fabric, the Applicant added a plastifying polymer to the coating composition. This plastifying polymer may be any organic thermoplastic polymer that is compatible or miscible with the PVDC or PVDC-based copolymer and has a glass transition temperature (T_(g)) lower than 40° C., preferably a polymer having a T_(g) comprised between −60° C. and +20° C.

Preferred plastifying polymers are selected from the group consisting of polyacrylates and polymethacrylates, styrene-butadiene copolymers, styrene-acrylate copolymers, polyvinyl acetate) and poly(ethylene vinylacetate) copolymers.

These plastifying polymers are added to the coating composition as a powder or aqueous polymer dispersion.

The organic polymer coating of the glass fiber mesh fabric preferably contains from 0.1 to 40 wt %, more preferably from 5 to 25 wt % and most preferably from 10 to 20 wt % of said plastifying polymer having a T_(g) lower than 40° C.

The present invention also provides a method for producing a coated glass fiber mesh fabric according to the present invention. This method comprises

-   (a) impregnating a woven or knitted uncoated glass fiber mesh fabric     with an aqueous coating composition containing, with respect to its     total solids content,     -   (i) from 60 wt % to 99.9 wt % of poly(vinylidene chloride)         (PVDC) or a copolymer thereof; and     -   (ii) from 0.1 wt % to 40 wt % of at least a second polymer         selected from the group consisting of melamine-formaldehyde         resins, phenol-formaldehyde resins, urea formaldehyde resins or         a combination thereof, -   (b) drying the impregnated glass fiber mesh fabric by heating at a     temperature comprised between about 100° C. and 280° C. for a period     of time comprised between about 30 seconds to 20 minutes.

Impregnation is preferably carried out by immersing the mesh fabric to be coated in an aqueous coating bath comprising the components of the organic coating and then pressing the impregnated fabric between to press rolls to eliminate excess coating composition. Impregnation could also be done for example by roll coating or screen coating.

The PVDC or PVDC-based copolymer is preferably used as an aqueous latex composition having total solids content comprised between 30 and 70 wt %, preferably between 40 and 60 wt %.

The other polymer components, i.e. formaldehyde-based resins and plastifying polymer are preferably added in aqueous forms (solutions or aqueous dispersions).

The coating bath may further comprise any useful adjuvant currently used in the field of polymer coatings such as thickeners, buffers, dyes, organic or mineral pigments, UV-absorbers, brighteners, rheology modifiers, alkali such as ammonia, fillers such as PVC or carbonates.

The resulting coated glass fiber mesh fabrics obtained by the above-described method have a gross heat of combustion (PCS) of less than 3.5 MJ/kg, preferably less than 3.0 MJ/kg (according to EN ISO 1716:2010).

EXAMPLES

The fiber mesh fabric for all examples was a standard glass fiber mesh fabric (Saint-Gobain Adfors) having a specific weight of 130 g/m².

This fabric was impregnated by immersion in an aqueous coating bath and then pressed between two rolls before being cured.

The coating baths had the following composition (% of solids)

-   A: 96.6% of an aqueous dispersion of PVDC (Diofan A063, SolVin)

3% of a melamine-formaldehyde resin

0.1% of aqueous ammonia

-   B: 76.9% of an aqueous dispersion of PVDC (Diofan A063, SolVin)     -   3% of a melamine-formaldehyde resin

20% of an acrylic binder (Printofix Binder CFN) with Tg of 20°.

0.1% of aqueous ammonia

The glass fiber mesh fabric coated with 7% (LOI) of composition A had a PCS of 1.4 MJ/kg.

The glass fiber mesh fabric coated with 7% (LOI) of composition B had a PCS of 2.9 MJ/kg.

The below table shows four comparative coating compositions resulting either in products having too high PCS or in products having poor mechanical strength:

Acrylic PVDC Melamine- Binder Comparative (Diofan formaldehyde (Printofix aqueous composition A063) resin Binder CFN) ammonia LOI C 100 — — 0.1% 20% D 50% 49.8 — 0.2% 10% E 50% 0% 50% 0.1% 10% F 60% 0% 40% 0.1% 10%

The glass fiber mesh fabric coated with 20% (LOI) of composition C had a PCS of 2.4 MJ/kg but inacceptable rigidity, brakes during bending, and has poor crosspoint stability

The glass fiber mesh fabric coated with 10% (LOI) of composition D had a PCS of 3.5 MJ/kg

The glass fiber mesh fabric coated with 10% (LOI) of composition E had a PCS of 6 MJ/kg

The glass fiber mesh fabric coated with 10% (LOI) of composition F had a PCS of 2.8 MJ/kg but a poor crosspoint stability 

1. A glass fiber mesh fabric coated with an organic polymer coating, wherein the organic polymer coating comprises: (i) from 60 wt % to 99.9 wt % of a poly(vinylidene chloride) (PVDC) or a copolymer thereof; and (ii) from 0.1 wt % to 40 wt % of a formaldehyde-based resin selected from the group consisting of a melamine-formaldehyde resin, a phenol-formaldehyde resin, a urea-formaldehyde resin and a combination thereof.
 2. The coated glass fiber mesh fabric according to claim 1, comprising from 6 wt % to 20 wt % of the organic polymer coating, measured as loss on ignition (LOI), relative to a total weight of the coated glass fiber mesh.
 3. The coated glass fiber mesh fabric according to claim 1, wherein the organic polymer coating comprises from 0.1 to 10 wt % of the melamine-formaldehyde resin or the phenol-formaldehyde resin or the urea-formaldehyde resin or a combination thereof.
 4. The coated glass fiber mesh fabric according to claim 1, wherein the organic polymer coating comprises a poly(vinylidene chloride) copolymer comprising from 75 to 98 wt % of vinylidene chloride monomer units and from 2 to 25 wt % of at least one comonomer selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, acrylonitrile, methacrylonitrile, an unsaturated carboxylic acid and vinyl chloride.
 5. The coated glass fiber mesh fabric according to claim 1, having a gross heat of combustion (PCS) of less than 3.5 MJ/kg (according to EN ISO 1716:2010).
 6. The coated glass fiber mesh fabric according to claim 1, wherein the organic polymer coating further comprises from 0.1 to 40 wt % of an organic polymer having a T_(g) lower than 40° C.
 7. The coated glass fiber mesh fabric according to claim 6, wherein the organic polymer having a T_(g) lower than 40° C. is selected from the group consisting of a polyacrylates, a polymethacrylate, a styrene-butadiene copolymer, a styrene-acrylate copolymer, a poly(vinyl acetate) and a poly(ethylene vinylacetate) copolymer.
 8. A method for producing the coated glass fiber mesh of claim 1, the method comprising: (a) impregnating a woven or knitted uncoated glass fiber mesh fabric with an aqueous coating composition comprising, with respect to total solids content, (i) from 60 wt % to 99.9 wt % of the poly(vinylidene chloride) (PVDC) or the copolymer thereof, and (ii) from 0.1 wt % to 40 wt % of at least a second polymer selected from the group consisting of a melamine-formaldehyde resin, a phenol-formaldehyde resin, a urea formaldehyde resin and a combination thereof; and (b) drying the impregnated glass fiber mesh fabric by heating at a temperature between about 100° C. and 280° C. for a period of time between about 5 seconds to 5 minutes.
 9. The method according to claim 8, wherein the poly(vinylidene chloride) or the copolymer thereof is an aqueous latex composition having a solids content between 30 and 70 wt %.
 10. The method according to claim 8, wherein the melamine-formaldehyde resin, the phenol-formaldehyde resin or the urea-formaldehyde resin is added as a non-cured aqueous solution of an oligomeric resin.
 11. The method according to claim 8, wherein the uncoated glass fiber mesh fabric has a weight of 30 to 500 g/m². 